Singapore Math Primary 5 Five Ratio Question

As my kid has been progressing through the Singapore school system, I've never been seriously challenged by primary school math until now. I was embarrassingly stomped by the following question.
It took me some time to figure it out. I've posted the question and answer for everyone's benefit.

Mr Lee had some red and white paint.  1/3 of the paint was red.  He used 
1/2 of the red paint and 5/6 of the white paint.  In the end, he had
a total of 10 liters of paint left.  How much paint did he have at first?

This question gave me a real headache until I found a way out. I've generated the solution in this pdf here